1. Field of the Invention
The present invention relates to an image display apparatus and, more particularly, to an image display apparatus which can display image information displayed on an image display element with a large field of view with high definition by utilizing a hologram optical element while making the entire apparatus compact.
2. Related Background Art
Conventionally, as an image display apparatus which allows a user to observe realistic image with a large field of view information displayed on an image display element such as a liquid crystal element as an image on a large screen, a large-scale CRT display apparatus, a projection TV apparatus, and the like are used.
These image display apparatuses suffer from the following problems. That is, such an image display apparatus requires a large space, and the surrounding area must be kept dark to satisfactorily observe image information.
In order to solve these problems, for example, as shown in FIG. 1, there is proposed an image display apparatus wherein a light beam from an image display apparatus is directly guided to eyes (the pupils of an observer) using an optical system arranged near the face of the observer.
Referring to FIG. 1, a liquid crystal display (liquid crystal panel) 201 displays image information on the basis of image data sent via a signal line 206. A backlight light source 204 illuminates the liquid crystal display 201. A light beam 208 based on image information displayed on the liquid crystal display 201 is reflected by a mirror 205 via an enlarging lens unit 203 consisting of concave and convex lenses, and is incident on the eyes (observation pupils) of an observer 210 as a reflected light beam 209.
At this time, the enlarging lens unit 203 displays, as a virtual image, image information displayed on the liquid crystal display 201 on a virtual image plane 202 a predetermined distance (e.g., 5 m) ahead of pupils 207 of the observer via the mirror 205. Thus, the observer recognizes, on the virtual image plane, image information displayed on the liquid crystal display 201. The term "observe" is hereinafter defined as "observe with recognition".
There is also proposed an image display apparatus, which allows an observer to personally observe image information such as a television image in an enlarged scale using an optical device 225 attached to his or her head, as shown in FIG. 2. Note that FIG. 2 is a perspective view of main part of the apparatus when viewed from the obliquely lower direction.
The main part of the image display apparatus shown in FIG. 2 will be described below. The apparatus includes liquid crystal color televisions 221R and 221L for the right and left eyes. Some light components of image information displayed on each of the liquid crystal color televisions 221R and 221L are reflected by a trapezoidal beam splitter 222R (and 222L, not shown) arranged in front of each eye, and are incident on a front concave mirror 223. The light beam reflected by the concave mirror 223 is transmitted through the beam splitter 222R (222L), and is incident on the corresponding eye of an observer (not shown). Thus, the observer recognizes image information displayed on the liquid crystal color televisions 221R and 221L as a virtual image at a predetermined position in front of the concave mirror 223.
At this time, in order to compensate for shortage of the number of pixels of the liquid crystal display panels and not to show a joint between pixels, pixel positions of the liquid crystal color televisions 221R and 221L are determined, so that their pixels are shifted from each other, and pixels are sampling-displayed to be further shifted from the pixel positions.
The image display apparatus shown in FIG. 1 has a small image display element, and the number of pixels thereof is limited. For this reason, when an image is to be displayed with a large field of view in an enlarged scale, an observer undesirably recognizes pixels, and it is difficult for the observer to observe high-quality image information.
For example, when a compact liquid crystal display is used as an image display element, most of existing liquid crystal displays have about 300,000 pixels. For this reason, the liquid crystal display has a resolution as low as that of an NTSC signal output from a video tape recorder, and it is very difficult to display such image information with a large field of view or with high definition.
In the image display apparatus shown in FIG. 2, two pieces of image information shifted from each other by about 0.5 pitches are respectively observed by the right and left eyes.
But, in general, when two pieces of image information are respectively input to the right and left eyes of a man, he or she searches and determines the corresponding origins of the two pieces of image information from his or her eyes, and thereafter, performs edge detection of each image information, differential processing for detecting a binocular parallax, and the like, thus recognizing the image information.
In view of such an image recognition mechanism of humans, it is very difficult to interpolate information between pixels by observing two pieces of pixel-shifted image information by the two eyes, and to recognize a single high-definition image.
In most of the methods of observing two pieces of pixel-shifted image information by right and left eyes, the corresponding origins of the two pieces of image information are merely determined to be shifted from each other, and it is difficult to recognize such image information as different pixel-shifted image information.